Skip to main content

Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

TALLOW

419

i

a, a thermometer c, reading to 0-2°, being arranged with its bulb exactly
in the centre of the liquid mass.   The whole is then left at rest.

The temperature is noted when the first crystals
appear at the bottom of the tube, crystallisation then
occurring at the surface of the liquid acids, on the walls
of the tube and in the mass of the liquid. When
numerous crystals appear throughout the liquid, the
mass is stirred gently with the thermometer until it
becomes pasty and opalescent and prevents the bulb
of the thermometer from being seen (stirring for 12-
15 seconds usually suffices) ; it is then left at rest.

Before and during the stirring the column of the
thermometer is carefully observed. It falls at first
slowly and regularly, but at a certain point the fall
slackens, then stops, and towards the end of the
agitation gives way to a rise to a maximum, the
latter persisting for about two minutes. This station-
ary temperature represents the solidifying point (titer)
of the fatty acids examined.1

The result is controlled by re melting—after some
time (preferably 12 hours)—the fatty acids at a tem-
perature not more than 5° above the solidifying point
found and allowing the molten mass to solidify in the
same conditions as before.

When the titer of a tallow is known, its yields of
liquid acids (oleic) and solid acids (stearic and pal-
mitic) may be deduced from Dalican's Table (XLVI), which has been
compiled empirically by mixing a typical commercial stearine with
solidifying point 54-4° with oleic acid freed from solid acids by pro-
longed standing and nitration. It indicates the percentages of stearic
and oleic acids in a tallow, a deduction of 4% having been made for the
glycerine and i% for moisture and impurities.

The percentage of stearic or oleic acid in a mixture of fatty acids is
given by the formula

a X 100

95 ~'
where a is the percentage of stearic or oleic acid given in Dalican's table.

2. Detection of Adulterations.—(a) Bone and wool fats: by the
odour. They lower the saponification number (especially wool fat) and
if the unsaponifiable matter is extracted, this contains a considerable amount
of cholesterol (see General Methods, 19).

(6) Palm oil and coco-nut oil; by the odour ; they raise the saponifi-
cation number, and the latter oil lowers the iodine number.

1 In place of the arrangement indicated above, Shukofi uses a vacuum-jacketed
vessel, into which 30-40 grams of the fused acid are poured. The vessel is then
closed with a stopper carrying a thermometer, and when the first crystals appear the
apparatus is shaken vigorously up and down until the contents become opaque. It
is then left at rest and the maximum temperature reached by the thermometer noierl.

FIG. 58 necessary, for a few moments). The tube is